Fats, Oils, and Plant Lipids
Fat is flavor, structure, and mouthfeel — and one of the trickiest things to mimic in plant-based cooking. In this module you'll learn the chemistry of fats, the personalities of plant oils, and the modern art of building animal-free fat from a liquid oil.
Learning objectives
- Describe the structure of a triglyceride and the difference between saturated, monounsaturated, and polyunsaturated fats.
- Explain why some plant fats are solid at room temperature and others aren't.
- Predict an oil's smoke point from its composition and refinement level.
- Distinguish O/W from W/O emulsions and identify common plant emulsifiers.
- Describe at least two ways a liquid plant oil can be turned into a butter-like solid without hydrogenation.
Fat: a structural primer
Most dietary fat is a triglyceride: a glycerol backbone with three fatty acid "tails" attached. The tails are long carbon chains, and what matters most is the bonds between those carbons:
- Saturated tails have only single bonds between carbons. They pack tightly and tend to be solid at room temperature. Coconut oil, cocoa butter.
- Monounsaturated tails have one double bond. The double bond creates a kink that prevents close packing. Liquid at room temp. Olive, avocado.
- Polyunsaturated tails have two or more double bonds. More kinks, more fluidity, but also more vulnerability to oxidation. Sunflower, flax, walnut.
Three fatty acid tails on a glycerol backbone. The kinks created by double bonds keep the molecules from packing tightly — and keep the oil liquid.
More saturation → harder fat at room temperature → more oxidatively stable, but typically less heart-healthy in the diet. The opposite for unsaturated.
Plant fats by personality
Every plant fat behaves differently in your kitchen. A short tour of the most important characters:
| Fat | Dominant fatty acid | Solid at 20 °C? | Best for |
|---|---|---|---|
| Cocoa butter | Stearic, oleic, palmitic | Yes (sharp melt at 34 °C) | Chocolate, vegan butter base, "snap" |
| Coconut oil | Lauric (saturated, medium chain) | Yes | Curries, baking, vegan butter, candies |
| Palm fruit oil | Palmitic + oleic | Semi-solid | Industrial spreads, frying — but see sustainability |
| Olive oil | Oleic (mono) | Liquid | Dressings, low/medium heat sautéing |
| Avocado oil | Oleic (mono) | Liquid | High-heat searing (refined version) |
| Sunflower (high-oleic) | Oleic | Liquid | Frying, baking |
| Flaxseed oil | Alpha-linolenic (omega-3) | Liquid | Cold dressings — degrades fast with heat |
| Sesame oil | Oleic + linoleic | Liquid | Finishing flavor; toasted version is aromatic |
Smoke point and oxidative stability
The smoke point is the temperature at which an oil begins to visibly smoke — meaning fatty acids are breaking down and free glycerol is becoming acrolein (the eye-stinging compound). It depends on the oil's:
- Refinement — bleaching and deodorizing strip away the small molecules that smoke first. Refined oils have higher smoke points than unrefined ones.
- Free fatty acid content — old, oxidized oils smoke earlier.
- Saturation — saturated oils are slightly more thermally stable.
Smoke point is not the same as oxidative stability over time. Polyunsaturated oils — even those with high smoke points — degrade quickly when exposed to heat, light, and air. Store them cold and dark.
Each frying cycle adds free fatty acids and oxidation products. The smoke point falls, the oil darkens, and off-flavors compound. Filter, cool, and reuse no more than 3–4 times for shallow frying.
Emulsions: oil and water, getting along
An emulsion is a stable dispersion of one liquid in another that wouldn't normally mix. Most food emulsions are:
- Oil-in-water (O/W): oil droplets suspended in a water-continuous phase. Vegan mayo, plant milk, salad dressing.
- Water-in-oil (W/O): water droplets in a fat-continuous phase. Vegan butter, margarine, ganache.
Both kinds need an emulsifier — a molecule with one end that likes water and another that likes oil. The emulsifier coats each droplet, lowering the energy cost of the interface so the system doesn't separate.
Plant-based emulsifiers worth knowing
- Lecithin (from soy or sunflower) — the workhorse. Used in chocolate, margarines, baked goods.
- Mustard powder — its mucilage and small proteins emulsify a vinaigrette beautifully.
- Aquafaba — small soluble proteins and saponins. The vegan mayo backbone.
- Mono- and diglycerides — common food additives derived from plant oils.
- Mucilage from flax or chia — polysaccharide-based, brilliant in dressings.
Emulsion explorer
Adjust droplet size and emulsifier coverage. Watch how a vinaigrette goes from a clear two-phase split to an opaque, stable mayonnaise — and breaks again when the emulsifier runs out.
Turning a liquid oil into a solid (without hydrogenation)
For most of the 20th century, the way to make a butter-like vegan spread was to hydrogenate a liquid oil — chemically saturating its double bonds until it solidified. The unfortunate side effect was trans fats, now known to harm cardiovascular health and largely banned from food.
Modern plant-based butters and shortenings sidestep hydrogenation in several ways:
- Blending naturally solid plant fats (coconut, cocoa butter, shea, palm) with liquid oils to hit a target solid-fat content at the desired temperature.
- Interesterification — rearranging the fatty acids on the glycerol backbones to change melting behavior, without creating trans fats.
- Oleogels — trapping a liquid oil in a 3-D scaffold of edible "structurants" like waxes (rice bran wax, sunflower wax), ethylcellulose, or even some proteins. The oil stays chemically liquid but behaves like a solid.
- Crystal templating — Miyoko's Creamery and others build vegan butters using cultured cashew cream + coconut oil + lecithin, structuring around a controlled crystal of the saturated phase.
Vegan butter isn't a single technology — it's a recipe for where the fat is solid and where it isn't. Get that profile right and the rest is flavor.
Kitchen Lab #3 — Vegan mayonnaise from aquafaba
~25 minWhat you'll learn
You'll build an oil-in-water emulsion using the proteins and saponins from chickpea brine. The blender's shear breaks oil into microscopic droplets; the aquafaba coats each one and prevents them from rejoining.
You'll need
- 60 mL aquafaba (the liquid drained from a can of unsalted chickpeas)
- 250 mL neutral oil (sunflower, grapeseed, refined avocado)
- 1 tsp Dijon mustard
- 1 tsp white-wine or apple-cider vinegar
- Salt to taste
- An immersion blender + tall narrow cup, OR a regular blender
Procedure
- Combine aquafaba, mustard, vinegar, and a pinch of salt in the cup.
- Pour the oil on top — yes, all of it. Do not stir yet.
- Set the immersion blender flat on the bottom of the cup. Run at full speed without moving for 15 seconds. You'll see a white emulsion form below the oil.
- Slowly raise the blender, drawing oil down into the emulsion until it's all incorporated (~30–45 seconds total).
- Taste. Adjust acid and salt. Refrigerate.
The science behind it
At rest, oil and water separate by gravity. The blender's blade creates such intense shear that oil droplets break down to micron scale — and aquafaba's surface-active molecules (small proteins, saponins) wrap each droplet in a stabilizing shell faster than they can recombine. Mustard reinforces the emulsion with its own mucilage, and the vinegar lowers pH to extend shelf life.
Diagnostic: a broken emulsion
If your mayo splits — fix it. Pour a fresh tablespoon of aquafaba into a clean cup, then slowly drizzle the broken mixture in while blending. You're starting a fresh emulsion and "lending" it the broken oil at a rate it can stabilize.
Discussion
Questions, corrections, or your own results from the lab? Drop them here. Comments are powered by GitHub Discussions via giscus; you'll need a free GitHub account.